Estimation of Taft ρ* of Dissociation Equilibriums of Methanium Ions RCH4+ the Hydrocarbon Super Acids: A Chemical Education Practice in Physical-Organic Chemistry Class-Room

Abstract

Background: In continuation from our crusade on the study of ‘attenuation effect' in aromatic and aliphatic systems prompted us to give another attempt to estimate the Taft ρ* value of the dissociation equilibriums (RCH4 + ⇌ RCH3 + H+) of the methanium ion (CH5 +) and substituted methanium ions (RCH4 + ) based on the attenuation effect on the dissociation equilibriums of alkyl ammonium ions (RNH3 + ⇌ RNH2 + H+) with one, two, three, four, five and six atoms between the ionizable proton and the first carbon atom of the substituent. Objectives: To explain the “attenuation effect” and its applications in organic chemistry to the graduate students. Methods: All calculations, drawings and curve fittings were done by KaleidaGraph software version 4.1 supplied by Synergy Software INC., Reading, PA, USA. Results: First the dissociation equilibriums of alkyl ammonium ions with increasing carbon chain length between the ionizable proton and the first carbon atom of the substituent were explained. The Taft ρ* was evaluated for all the equilibriums. Finally the effect of number of atoms between the ionizable proton and the first carbon atom of the substituent were studied. From this the ρ* was evaluated for the equilibrium (RCH4 + ⇌ RCH3 + H+ was evaluated. Conclusion: Using the application of “attenuation effect” the experimentally not determinable quantities could be determined. Keywords: Taft reaction constant (ρ*), attenuation effect, methanium ions, super acids, protonation, methananium ions.